KINETIC-MODEL OF AU-GAAS INTERFACIAL REACTION

Open-system annealing of Au/GaAs leads to vaporization of As species and migration of Ga atoms into Au. These processes are simultaneous only on a macroscale. A simple kinetic model is developed in which they are treated sequential by introducing specific fluxes F(Ga) and F(As). In view of a high diffusivity of Ga in Au, F(Ga) is calculated assuming linear flow at the phase boundary. F(As) is set constant for a given external pressure of arsenic. Conservation of bulk stoichiometry of GaAs implies that the decomposition rate of GaAs is controlled by the slower process. The model accurately describes the observed reaction rate in both capped and open configuration. It is shown that, upon heating, the instantaneous composition of the GaAs surface in contact to the metal evolves from initially As rich to Ga rich when Au becomes saturated with Ga.